When a collection of monsters have a party and spend the evening dancing with no regard for others

oh my god Nigel, the monsters next door are having a monster mash again they will keep us up all night again.
Can you go around and have a word with the chief monster 'Paul' and ask him not to make them strange ape noises again

when you are trying to have sex with a girl but you don;t have a full erection, so you grab and squeeze the base of your dick and try to 'mash' it into the girl in hopes of stuffing it in and getting an erection

beau was having trouble dr'ing this girl because he was too drunk, so he used the monster mash method.